Smoke from a rash of wildfires in Canada and northeast Minnesota is about to sweep into the Great Lakes and Northeast, potentially leading to unhealthy air quality from the upper Midwest to the mid-Atlantic states and New England.

Where the fires are right now

The map below shows locations of 800 active Canadian wildfires, most numerous from the Northwest Territories to northern Saskatchewan, northern Manitoba, western Ontario, northern Quebec and Labrador.

And Monday, triple-digit heat, winds and low humidity triggered a major flare-up of wildfires that had been burning since May in northeast Minnesota, prompting temporary closure of the Boundary Waters Canoe Area and a peacetime emergency declaration from Gov. Tim Walz.

The Minnesota Pollution Control Agency has already issued an air quality alert for northeast Minnesota through Thursday.

Statewide air quality alerts have also been issued in both Michigan and Wisconsin.

(MORE: The Weather Company Labs: active wildfires & fire weather tracker)

Midwest, Northeast smoke forecasts

Unfortunately, winds out of the northwest will push this wildfire smoke from Canada and northeast Minnesota into the Great Lakes and Northeast beginning Wednesday.

And this smoke may reach the ground in some areas, leading to potentially unhealthy air quality for several days. Here's the timeline of when surface wildfire smoke may be a problem.

Wednesday

The densest smoke will likely be in the Great Lakes closest to the wildfires, from northern Minnesota to northern Wisconsin, Michigan's Upper Peninsula and at least northern Lower Michigan. It's in these areas where air quality could become unhealthy for all, not just sensitive groups.

Some near-surface smoke could also invade parts of the Northeast, including parts of New England, New York, including the New York City tri-state area and northern Pennsylvania. Some of this smoke could at least be unhealthy for sensitive groups.

(WATCH: What air quality index forecasts mean)

Thursday and beyond

Near-surface smoke may be more widespread from the upper Midwest through the Great Lakes and much of the Northeast Thursday, possibly as far south as northern Illinois, northern Indiana, Ohio, West Virginia, Virginia and Maryland.

Again, the surface smoke likely will be most dense in the northern Great Lakes.

But at least some smoke could make the air unhealthy at least for sensitive groups along much of the Interstate 95 corridor, including New York, Philadelphia, Baltimore and Washington, D.C.

This ground smoke may also be unhealthy in Buffalo, Chicago, Cleveland, Detroit, Milwaukee, Pittsburgh and the Twin Cities, Thursday.

Some unhealthy ground smoke may linger in parts of the Midwest and Northeast into Friday, as well.

What you need to know to stay safe

Wildfire smoke is hazardous to breathe for several reasons.

It contains microscopic "particulate matter" much smaller than the width of a human hair that can lodge deep into the lungs and then enter your bloodstream.

It can lead to short-term effects, such as coughing, shortness or breath, a scratchy throat, runny nose and burning eyes.

Prolonged exposure to dense smoke can increase the risk of chronic lung issues and increase inflammation that could lead to heart attacks and strokes.

If you're in these affected areas in the Midwest and Northeast, check your air quality forecast before heading outside.

You can do that on The Weather Channel app by going to your local forecast, then tap the "Breathing" button. Or, from your local forecast page on weather.com, click on the "Air Quality" button at the top.

The index is color coded from green (good) to maroon (hazardous).

If your air quality forecast is....

• At least code orange: More sensitive groups such as those with respiratory or heart conditions, the elderly, children and those pregnant should avoid staying outside more than necessary.
• Code red, purple or maroon: Everyone should limit their time outdoors. Consider exercising indoors and if you need to walk your pet outside, do so as briefly as possible.

(MORE: How air pollution affects you)

Why the smoke?

Plumes of smoke generated by larger wildfires are steered by winds from the ground to the top of the smoke plume.

In this case, the heat dome responsible for the recent record heat in the northern U.S. will get squashed into the Carolinas, setting up a northwesterly wind flow in the upper levels of the atmosphere.

That will allow a pair of cold fronts to sag into the Midwest and Northeast.

Northwest winds behind those fronts will tap smoke from those wildfires not just in western Ontario and northeast Minnesota, but also potentially some lofted smoke from additional fires in northern Canada.

So, while these weaker cold fronts bring relief from heat and humidity, they may also usher in some wildfire smoke, both aloft and at the ground. This is a scenario that has occurred several past summers this decade and is a pattern we were concerned about this summer during a developing, strengthening El Niño.

(MORE: This $65 DIY air filter builds in just 15 minutes)

Jonathan Erdman is a senior meteorologist at weather.com and has been covering national and international weather since 1996. Extreme and bizarre weather are his favorite topics. Reach out to him on Bluesky, X (formerly Twitter) and Facebook.​